LCD TV at this stage at present, there are two ways of dimming for liquid crystal display televisions. One is direct current dimming and the other is PWM dimming. The PWM dimming causes the current flowing through the LED string constantly turning on and off through the high-frequency switch. By controlling the duty ratio of the light string conduction, the brightness adjustment can be achieved. Thus, in the PWM dimming process, the LED light-emitting diode actually keeps flashing. In order to avoid the recognition range of the human eye, the TV manufacturers generally raise the dimming frequency up to 100 Hz or more. The DC dimming achieves dimming with the linear adjustment of the current of the LED string. There is no switch in the DC dimming and no-flicker dimming can be realized. Most of the LED driving chips with analog dimming capability require DC positive dimming (dark at low voltage level and bright at high voltage level). However, for a portion of television main chips, the DC negative dimming (bright at low voltage level and dark at high voltage level) is more conducive to the system design. However, the main chip dimming signal cannot be directly supplied to the LED backlight control chip, which cannot meet the requirements of the TV system to the DC negative dimming.